Fix a broken link in Aggregation (Part 2.4)

Author: jackeys

Part 2 - Sequence Basics/4. Aggregation.md

@@ -559,7 +559,7 @@ Observable.range(0, 3)
 2
 ```
 
-Nesting observables to consume them doesn't make much sense. Towards the end of the pipeline, you'd rather flatten and simplify your observables, rather than nest them. Nesting is useful when you need to make a non-nested observable be of the same type as a nested observable that you have from elsewhere. Once they are of the same type, you can combine them, as we will see in the chapter about [combining sequences](/Part 3 - Taming the sequence/4. Combining sequences.md).
+Nesting observables to consume them doesn't make much sense. Towards the end of the pipeline, you'd rather flatten and simplify your observables, rather than nest them. Nesting is useful when you need to make a non-nested observable be of the same type as a nested observable that you have from elsewhere. Once they are of the same type, you can combine them, as we will see in the chapter about [combining sequences](/Part%203%20-%20Taming%20the%20sequence/4.%20Combining%20sequences.md).